Large scale cylindrical cloak in free space without superluminal propagation

Abstract

Despite its remarkably fast development in the past few years, the technology of invisibility cloaking is still facing many serious bottlenecks, e.g. the bandwidth, the superluminal limitation, dispersion, loss, etc. In this paper, we experimentally demonstrated an alternative approach of invisibility cloaking that can combine technical advantages of all current major cloaking strategies in a unified manner and thus can solve bottlenecks of individual strategies. A broadband cylindrical invisibility cloak in free space is designed based on scattering cancellation (the approach of previous plasmonic cloaking), and implemented with anisotropic metamaterials (a unique property of previous transformation-optics cloaking). Particularly, non-superluminal speed of light in the cloak, a superior advantage of non-Euclidian conformal mapping cloaks, is inherited in this design, and thus is the reason of its relatively broad bandwidth. This demonstration provides a possibility for future practical implementation of cloaking devices at large scales.